In Shame, Matthew Fassbender plays a sex-addicted New Yorker whose physical and psychological hungers drive him to the point of self-annihilation.

Fox Searchlight Pictures

The Irish actor Michael Fassbender stars in two current films that revolve around the perils of sex — which means you see him have a lot, so he'll have something to regret.

You know how the sex will play out in Shame, because of, well, the title. Fassbender plays a sex addict, Brandon Sullivan, born in Ireland, raised in New Jersey, and he seems to work in advertising, which is unfortunate since he resembles Mad Men's John Hamm.

Brandon's not a predator — he's magnetic enough that his pick-ups are soft sells. But he prefers prostitutes and online chats: nothing involving emotional commitment. His one tie is to his sister, played by Carey Mulligan, a nightclub singer who sleeps around but, unlike her brother, gets too emotionally committed too fast. Each sibling embarrasses the other, but they're stuck together.

Shame has full-frontal nudity and a rare NC-17 rating, although the shots in question aren't necessary and make me think they're there so the director can say, "The actors are naked, I tell you. Emotionally and physically." His name is Steve McQueen — the British art-school graduate, not the late American actor, obviously — and he films his characters like specimens in a jar.

There are several excellent scenes, one wordless: Brandon stares at a woman on the subway, mentally undressing her, and she, after much hesitation, seems to mentally undress him back. I bet the actress, Lucy Walters, will get parts after this. The other great scene is early, when Brandon overhears his sister pleading on the phone with a lover not to leave. Mulligan hits startling notes as she sobs; her fear of separation is primal.

But the film's trajectory is so obvious I found myself laughing, especially when Brandon flees a potential girlfriend and sinks to what is plainly depicted as a new low: He goes to a gay bar and lets an anonymous man... "It's too tragic," the film seems to be saying. Then he has an orgy where's he's photographed like Christ in agony on the cross. But since McQueen has told you little of Brandon's or his sister's past, you get no insight into how they turned out the way they did. It's empty sex for us, too.

With a mustache and specs, Fassbender plays Carl Jung to Viggo Mortensen's Sigmund Freud in A Dangerous Method, directed by David Cronenberg from a script by Christopher Hampton. It begins with Jung's patient Sabina Spielrein, a disturbed Russian Jewish woman, driven to a hospital screaming her head off. She's played by Keira Knightley in a style that would seem big from the third balcony, spitting out her consonants and working her long jaw so hard it hurts to look at her. But I admire Knightley's guts; she physicalizes every emotion, a nice contrast to the all the repression going on in the other characters.

Jung begins as an eager protege of the older Freud, with whom he dines in Vienna, where they speak of this strange new field of psychotherapy. Mortensen is a model of witty restraint: His Freud studies people with amusement, puffing on a cigar that's not just a cigar, since he looks like he's having dirty thoughts. That's one source of the rift between him and Jung, who's open to mysticism and the supernatural, who doesn't want sex to be the only explanation for how people behave.

But sex looms pretty large in A Dangerous Method. Goaded on by a patient who's also a therapist (he's played with delicious lewdness by Vincent Cassell), Jung pursues an S&M affair with Sabina — who then becomes a therapist herself and tries to convince Freud that the sex drive is demonic and self-annihilating. He listens, studying her, puffing on his cigar.

On first viewing, I found A Dangerous Method a wordy bore, but I saw it again after seeing Shame and did ... not a 180, but at least a 160-degree turnaround. That wordiness, coupled with Cronenberg's classical restraint, is part of a splendid Freudian joke at the movie's center. It's fun to watch these eggheads try so earnestly to create a theoretical framework for their sexual impulses — as opposed to, say, Fassbender's sex addict in Shame, who unemotionally acts them out, and proves no more interesting than a zombie.